Retaining wall paint bubbles?

I am working on four 2' tall by 40' long retaining walls, block which has been smoothed over with plaster of some sort. The original paint was elastomeric and was applied when the walls were new, roughly 12 years ago. The walls had supposedly been tarred from behind before dirt fill. The paint has bubbled evidently since new, I'm guessing because the water from behind cannot permeate through the paint. I have fixed the bubbling but it reappears within weeks. I had a mason drill 1" holes every few feet at the bottom of one wall to see if having some drainage helps. Is this the correct solution? If there are other solutions you may know of I've been battling this for 6 months now, and any help is greatly appreciated!